1. Field of the Invention
The present invention relates to ion selective electrodes and more specifically to ion selective electrodes for detecting organic drugs in saliva, sweat, and surface wipes.
2. Description of the Related Art
It is currently estimated that there are over three million hardcore cocaine users and one million hardcore heroin users in the United States. It is also estimated that there are over two million occasional cocaine users and half a million occasional heroin users. Together they consumed 269 metric tons of cocaine and 12.9 metric tons of heroin in 2000 spending $63 billion on illicit drugs. Rhodes, W., Layne, M., Johnston, P., Hozik, L., What America's Users Spend on Illegal Drugs 1988-1998, Office of National Drug Control Policy, December 2000. One adverse consequence of drug use that appears to be grossly under-publicized is driving under the influence of drugs. Although alcohol contributes to about 39% of the 40,000+ annual fatal traffic accidents and 1.4 million arrests per year, a substantial fraction of those under the influence of alcohol are also under the influence of drugs. Shults, R., Impaired Driving, Dec. 11, 1998, CDC, National Center for Injury Prevention & Control. In a recent study conducted in Nassau County, N.Y. and Houston, Tex., about 36% of 800 drivers arrested for driving while intoxicated also had drug metabolites in their urine. See Hersch, R. K., Crouch, D. J., and Cook, R. F., “Field Test of On-Site Drug Detection Devices,” DOT HS 809-192, October 2000 and Brookoff, D., Cook, C. S., Williams, C., and Mann, C. S. “Testing Reckless Drivers for Cocaine and Marijuana”, N Engl J Med, 331(8):518-522 (1994) for similar results. Another study showed that 45% of federal prisoners have driven a car while under the influence of drugs (www.ojp.usdoj.gov/bjs). Thus, driving under the influence of drugs (DUID) is a critically important public safety issue.
Campaigns such as Mothers Against Drunk Driving have reduced alcohol-related automobile fatalities over 30% in the past decade. One of the factors that appears to dissuade public interest groups from starting similar campaigns against DUID is the lack of effective tools in the hands of law enforcement officers to rapidly and privately measure drug levels. Once those tools are made widely available, a serious and credible deterrent to occasional drug use would be present. The publicity would both reduce DUID and help make illicit drug use socially unacceptable in the public eye.
During routine traffic stops or DWI (driving while intoxicated) roadblocks, police officers have only a few moments to determine if a driver is under the influence. Besides the usual visual clues, the main tool in current use is the Officer's sense of smell, which works in a limited way only for alcohol and marijuana. Frequently, individuals who consume drugs also consume alcohol, which provides a synergistic effect. If the alcohol level is below the legal limit, the police officer must make a decision on an arrest. Other drugs of abuse do not provide overt signs of use unless an individual is substantially impaired. Thus, a rapid, fieldable instrument assisting in this decision process would help detect and deter DUID if widely employed.
Urine and blood can be tested to detect drug use. However, the non-private collection method and the long window of detection of drugs in urine (days to weeks) are considered by many to be an invasion of privacy and may not be reflective of the actual safety hazard posed by use of drugs while driving.
Other media, such as saliva and sweat, can also be tested to detect drug use. As shown in FIG. 1, after the first few minutes of use, levels of cocaine in saliva parallel levels in plasma, which are better associated with impairment. If a cocaine cut-off level were set at approximately 50 ng/mL, the window of detection for cocaine in saliva would only be four hours. Because cocaine can only be detected during this short time-frame following cocaine administration, it is easier to demonstrate some impairment in driving performance compared to the several days that urine would test positive. In some operational scenarios, saliva may be too intrusive. Instead, a skin swab may be employed. Although skin swabs measure both passive exposure and use, the absence of drug residues would rule out drug use, except under extraordinary circumstances.
Current technologies to detect drugs in saliva include ion mobility mass spectrometry and immunoassays. Ion mobility mass spectrometry, as exemplified by the Barringer Ion Scan and the Barringer Sabre 2000 (www.barringer.com) or the Ion Track Itemiser and the Ion Track VaporTracer-2 (www.iontrack.com), has the advantage of rapid (1 minute) detection of a wide variety of materials in a semi-quantitative manner. However, it has the disadvantages of high cost ($20K-$42K/unit), maintenance, and bulk (shoe-box to suitcase sized). Immunoassays, as exemplified by Securetec Drugwipes (www.securetec.net), have the advantage of simplicity of operation, portability, and low cost (<$10/each). U.S. Pat. No. 5,891,649, incorporated herein by reference, discloses the use of immunoassays for detection of drugs in sweat. However, immunoassays are selective for each drug or drug class, and therefore, a separate test must be performed for each substance suspected. Also, they are non-reusable so the reoccurring costs may be prohibitive in high volume applications. In addition, immunoassays only provide a presence or absence indication; quantitative analysis is difficult without instrumentation and then it is linear only over a limited range.
Another technology to detect drugs is ion selective electrodes, which measure ionic species. Ion selective electrodes are well known in the art to measure ionic species such as potassium, lithium, sodium, and calcium. However, developing ion selective electrodes to detect drugs has been limited to detecting drugs in pharmaceutical preparations or to detecting illicit drugs in urine or blood. Information relevant to using ion selective electrodes can be found in the following references: Elnemma, E. M., Hamada, M. A. and Hassan, S. S. M., “Liquid and Poly (Vinyl Chloride) Matrix Membrane Electrodes for the Selective Determination of Cocaine in Illicit Powders,” Talanta, 39 1329-1335 (1992); Campanella, L., Colapicchioni, C., Tomassetti, M., Bianco, A. and Dezzi, S., “A New ISFET Device for Cocaine Analysis,” Sensors and Actuators, 24-25 188-193 (1995); Watanabe, K., Okada, K., Oda, H., Furuno, K., Gomita, Y. and Katsu, T., “New Cocaine-Selective Membrane Electrode,” Analytica Chimica Acta, 316 371-375 (1995); K. Watanabe, K. Okada, and T. Katsu, “Development of an Amphetamine-Selective Electrode,” Jpn. J. Toxicol. Environ. Health, 42, 33 (1996); S. S. M. Hassan and E. M. Elnemma, “Amphetamine Selective Electrodes Based on dibenzo-18-crown-6 and dibenzo-24-crown-8 Liquid Membranes,” Anal. Chem., 61 2189-2192 (1989); K. Watanbe, K. Okada, H. Oda, and T. Katsu, “Development of a portable cocaine-selective electrode,” Jpn. J. Toxicol. Environ. Health, 43, 17(1997); L. Campanella, L. Aiello, C. Colapicchioni, and M. Tomassetti, “Lidocane and Benzalkonium Analysis and Titration in Drugs Using New ISFET Devices,” J. Pharm. Biomed. Anal., 18 117-125 (1998); L. Campanella, C. Colapicchioni, M. Tomassetti, and S. Dezzi, “Comparison of Three Analytical Methods for Cocaine Analysis of Illicit Powders,” J. Pharm. Biomed. Anal., 14 1047-54 (1996); S. S. M. Hassan, E. M. Elnemma, and E. H. El-Naby, “Solid State Planar Microsensors for Selective Potentiometric Determination of Ethylmorphine,” Anal. Let., 32 271-285 (1999); E. M. Elnemma and M. A. Hamada, “Plastic Membrane Electrodes for the Potentiometric Determination of Codeine in Pharmaceutical Preparations,” Mikrochim Acta, 126 147-151 (1997); L. Cunningham and H. Freiser, “Ion-Selective Electrodes for Basic Drugs,” Anal. Chim. Acta., 139 97-103 (1982); C. R. Martin and H. Freiser, “Ion-Selective Electrodes for the Determination of Phencyclidine,” Anal. Chem., 52 1772-1774 (1980); G. D. Carmack and H. Freiser, “Assay ofPhenobarbital with an Ion-Selective Electrode,” Anal. Chem., 49 1577-1579 (1977); Cosofret, V. V. and Buck, R. P., “Recent Advances in Pharmaceutical Analysis with Potentiometric Membrane Sensors,” Critical Reviews in Analytical Chemistry, 24, 1-58 (1993); K. Watanbe, K. Okada, H. Oda, and T. Katsu, “Development of a Portable Cocaine-Selective Electrode,” Bunseki Kagaku, 46 1019-1023 (1997); S. Komorsky-Lovric, I. Galic, and R. Penovski, “Voltammetric Determination of Cocaine Microparticles,” Electroanalysis, 11 120-123 (1999); T. Yeow, M. R. Haskard, D. E. Mulcahy, H. I. Seo, and D. H. Kwon, “A Very Large Integrated pH-ISFET Sensor Array Chip Compatible with Standard CMOS Processes,” Sensors Actuators B 44 434-440 (1997); U.S. Pat. No. 5,522,978; U.S. Pat. No. 5,914,271; U.S. Pat. No. 5,180,481; U.S. Pat. No. 6,212,418; U.S. Pat. No. 6,087,182; U.S. Pat. No. 6,165,796; U.S. Pat. No. 6,033,914; U.S. Pat. No. 5,531,870; U.S. Pat. No. 5,554,339; U.S. Pat. No. 5,753,519; U.S. Pat. No. 4,713,165; U.S. Pat. No. 4,454,007; and U.S. Pat. No. 4,399,002, all of which are incorporated herein by reference.